The present invention relates to a cooling system for vehicles, and more particularly, to a system in which a water pump additionally performs functions of a thermostat so that a structure of the cooling system can be simplified.
Generally, as shown in FIG. 1, a conventional cooling system comprises a water pump 1 that forces coolant through an engine and other system parts, a thermostat 2 that controls coolant flow and engine operating temperature, a radiator 3 that transfers engine coolant heat to outside air, and radiator hoses 4 that connect an engine 5 to the radiator.
The water pump 1 comprises an impeller that forces coolant through the engine block, cylinder head, and radiator. A water pump pulley is connected to an engine crankshaft pulley via a fan belt so that the spinning engine crankshaft pulley causes the fan belt to turn the water pump pulley, pump shaft, and the impeller. The water pump 1 spins and produces coolant pressure and flow using the impeller.
To minimize an amount of exhaust gas during cold starting and to improve engine durability, when the engine is cold the thermostat 2 is closed and coolant cannot circulate through the radiator 3. Instead, the coolant circulates around inside the engine block, cylinder head, and intake manifold until the engine is warm. As the coolant becomes hot, the thermostat gradually opens and allows coolant to flow through the radiator so that the coolant temperature is maintained to a certain level.
However, when the engine is at low rpm, friction force between the impeller and the coolant becomes relatively larger, and therefore engine load increases so that fuel economy becomes poor.
Further, in the conventional cooling system, the thermostat and the water pump exist separately so that the cooling system becomes complicated, and also engine power is diminished because of driving the water pump while the thermostat is closed.
The present invention provides a cooling system in which unnecessary power loss can be decreased. According to a preferred embodiment, the cooling system of the present invention comprises a radiator that transfers coolant heat to outside air, a water pump that is mounted to an engine and forces coolant through an engine and other system parts. Preferably the water pump comprises a housing that forms a main body of the water pump and is mounted on an engine cylinder block that is provided with a plurality of coolant passageways, a pulley that transfers turning force from the engine crankshaft to the water pump, a first impeller that forces coolant to circulate through the engine, a pump shaft that is rotatably mounted to the housing, one end of which is fixedly connected to the pulley, the other end of which is fixedly connected to the first impeller, a second impeller that forces coolant to circulate through the engine and the radiator, and a second impeller rotating means that selectively rotates the second impeller according to a coolant temperature.
In an alternative embodiment, a water pump according to the invention comprises a housing, first and second impellers and a temperature responsive linkage between the impellers. The housing supports a pump shaft and other conventional components of a water pump. The first impeller is mounted on the pump shaft to circulate coolant through associated engine coolant passageways as is known in the art. The second impeller supported by the housing to circulate coolant through associated radiator coolant passageways. The temperature responsive linkage is disposed between the second impeller and pump shaft carrying the first impeller to engage the second impeller when coolant temperature rises above a predetermined value.
In a preferred embodiment, the temperature responsive linkage comprises first and second friction plates acted on by biasing members and a heat expansive member. The first friction plate is mounted to the pump shaft. The second friction plate is mounted adjacent to the first friction plate, to rotate with the second impeller. At least one biasing member is disposed to force apart the first and second friction plates in a default condition. The heat expansive member acts in opposition to the at least one biasing member when the coolant temperature rises above a predetermined value. At this point the heat expansive member exerts a force overcoming the biasing member such that the first and second friction members are forced together for rotation of the second impeller. Preferably the biasing members are springs and the heat expansive member is a member filled with a fluid that expands when heated, such as wax.